Submersible pumping systems are often deployed into wells to recover petroleum fluids from subterranean reservoirs. Typically, the submersible pumping system includes a number of components, including one or more fluid filled electric motors coupled to one or more high performance pumps. Each of the components in a submersible pumping system must be engineered to withstand the inhospitable downhole environment.
Components commonly referred to as “seal sections” or “motor protectors” protect the electric motors and are typically positioned above the motor. These components provide several functions, such as transmitting torque between the motor and pump, restricting the flow of wellbore fluids into the motor, protecting the motor from axial thrust imparted by the pump, and accommodating the expansion and contraction of motor lubricant.
By way of illustration, FIG. 1 shows a prior art submersible pumping system 200 disposed in a wellbore 202, and includes an electric motor 204, a pump 206, and a seal section 208. The submersible pumping system 200 is attached to production tubing 210, which provides a conduit for producing fluids to the surface.
Torque is generated in the motor 204 and transmitted to the pump 206 by a shaft in the seal section 208. Since the shaft is a potential leak path by which corrosive wellbore fluids can reach the motor 204, the seal section 208 is designed to limit the flow of wellbore fluids along the shaft.
The seal section 208 also protects the motor 204 from axial thrust and shock created by the pump 206. The pump 206 pulls in wellbore fluids and propels the fluids up the production tubing 210, creating axial thrust that can damage the motor 204. The seal section 208 absorbs some of this thrust, providing a barrier between the motor 204 and the pump 206.
Heat in the wellbore and heat generated by the motor 204 during operation cause the lubricating oil to expand in the oil filled motor 204. Excessive expansion of the lubricating oil can cause damage to the motor if the lubricating oil is not allowed to escape. As a safeguard, the seal section 208 provides a means by which the oil can escape, preventing the accumulation of excessive pressure inside the motor 204.
Similarly, the seal section 208 also provides a means for accommodating contraction of the lubricating oil during cooling. As the lubricating oil contracts, wellbore fluid is drawn into the seal section 208 to maintain the appropriate pressure gradient between the motor 204, the seal section 208 and the wellbore. The seal section 208 is also designed to segregate the lubricating oil and the wellbore fluid to avoid contamination of lubricating oil in the motor 204.
Alternate configurations of the pump and motor may also be desirable in a wellbore tool string. For example, in some wellbore operations, fluids are forced down the well from one zone to another. In these operations, it is often desirable to place the pump below the motor at the bottom of the tool string. This configuration increases the risk that wellbore fluids will migrate upward from the pump into the motor. The motor may also be subjected to increased axial thrust from the pump located at the bottom of the tool string. There is therefore a need for protecting the motor from axial thrust and wellbore fluid contamination in configurations where the pump is located below the motor. It is to these and other deficiencies in the prior art that the present invention is directed.